cgroup/freezer: add per freezer duty ratio control

From: Jacob Pan <[email protected]>

Fixing subject in cover letter, should be v4 instead of v3

Changelog:
v9: - merged duty ratio related data structs
- removed toggling bit, replaced with freezer->state
- consolidated toggling mode cancellation function
- use spin lock to protect duty ratio parameter writes
- use second as period
- allow 0% and 100% frozen time, aligned behavior with freezer_write()
v8: - minor clean up
v7: - use delayed workqueue instead of per cgroup kernel thread
to manage toggling
- make freezer.state higher priority than duty ratio setting
- small correction in documentation

v6: - remove check for duty ratio == 100 case
v5: - improve error handling in duty ratio/ period writes
- fix the logic to avoid kthread creation when ratio and period are invalid.
- 100% frozen is not permitted in duty ratio set up

v4: - limit kthread creation only when valid duty ratio
parameters are given.
- changed period back to milisecond
- consolidated paramter write functions

v3: - added documentation

v2:
- use read_u64/write_u64 instead of string read/write
- use period in second instead of ms
- renamed duty_ratio to duty_ratio_pct, be more specific
- removed locking around period and duty_ratio reads

Jacob Pan (1):
cgroup/freezer: add per freezer duty ratio control

 Documentation/cgroups/freezer-subsystem.txt |   23 ++++++
 kernel/cgroup_freezer.c                     |  109 ++++++++++++++++++++++++++-
 2 files changed, 130 insertions(+), 2 deletions(-)